This invention relates to liquid ink compositions for use in ink jet recording apparatus and, in particular, to a liquid ink composition having a reduced sodium ion concentration in order to prevent insoluble particles from leaching into the ink from ink pouches or tanks in which the ink is stored.
Conventional ink jet printers achieve quiet, high speed, high quality color printing using a variety of ink droplet ejection techniques including continuous ink jet ejection, impulse ink jet ejection, thermal ink jet ejection and the like. These techniques generally eject ink droplets from an extremely minute nozzle orifice having a diameter between about 10 and 100 .mu.m. In order to pass through the minute nozzle orifice or ink flow path the ink must be clean and stable.
Ink is generally prepared in a clean room in order to minimize the introduction of dust particles. Alternately, the prepared ink is filtered through a membrane filter having a mesh size of 1 .mu.m or less. In addition, tanks for storing ink are cleaned with ultrapure water using a precision cleaning process prior to being filled.
In conventional ink tank systems having a liquid ink stored therein, the ink is clean only when it is first introduced into the tank. After a period of time, at least in part due to changes in environment, including temperature, the composition of the ink deteriorates as a result of elution of material from the ink tank into the ink. This material reacts chemically with the ink composition to form insoluble substances and these insoluble substances clog the minute paths, filters, orifices, nozzles and the like of the ink jet printer. Consequently, ink flow is interrupted and print quality deteriorates resulting in a dot missing.
It is, therefore, desirable to provide an ink composition wherein insoluble substances are not produced when the ink is stored in an ink tank for an extended period of time.